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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Conversions >> RE: Ryobi 31 cc Conversion
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RE: Ryobi 31 cc Conversion - 6/21/2005 7:48 AM   
I_Fly_Coolers


 

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From: winter park, FL, USA
Status: offline 		I have 2 of these Ryobi's and the 18x8 seems to work best. For starting, I git rid of the primer bulb and the choke. I put my finger over the carb, turn prop slowly over by hand until my finger is wet with fuel. Toggle kill switch to "run" 1/3 throttle, quick hit with an electric starter, fires right up every time.

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RE: Ryobi 31 cc Conversion - 6/22/2005 4:12 AM   
Hircflyer



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Status: offline 		Carb very difficult to get to.....................mounted on back of crankcase on this engine........only have about 1/2 inch between carb and firewall can't get my fat finger in there.

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RE: Ryobi 31 cc Conversion - 6/22/2005 4:50 AM   
av8tor1977



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Status: offline 		Once upon a time in these forums someone had a pic of a popsicle stick with half of a small rubber ball glued to it for choking Ryobis. Looked like a pretty simple and good idea to me.

AV8TOR

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RE: Ryobi 31 cc Conversion - 6/22/2005 4:52 AM   
I_Fly_Coolers


 

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Status: offline 		Uh-Oh!! Yes, mine have rear carb as well- but I installed mine with the flat mount, hole in firewall where carb sticks through- then a hole cut on top behind cowl to get my finger over the carb. If you can rig a push-pull wire to the choke, that would work too, except you really need a 100% seal to get the fuel sucking through the fuel line.

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RE: Ryobi 31 cc Conversion - 6/22/2005 5:02 AM   
Hircflyer



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Status: offline 		You guys have just inspired me!!! I'm going to try an ear plug glued to a popsicle stick..........

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RE: Ryobi 31 cc Conversion - 6/22/2005 5:22 AM   
I_Fly_Coolers


 

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Status: offline 		That sounds like an idea!!! Remember, once the carb is wet- 1/3 throttle, bump it with an electric starter and that should be all it takes. Also, be sure the line from the carb to what used to be the primer bulb is blocked off- I use a short piece of gas line with a screw in the end.

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RE: Ryobi 31 cc Conversion - 9/8/2006 3:04 PM   
dswarrenga


 

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Status: offline 		Can someone please tell me what Walbro or Zama carb I should be using on a Ryobi 31cc (725r) conversion. I bought the converted engine but it needs a carb. thanks in advance!

David Warren

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RE: Ryobi 31 cc Conversion - 9/8/2006 7:48 PM   
flyjoe540



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Status: offline 		any walboro or zama from 9 mm to 11.5mm at the venturie seems to be the general consensus. the stock ones are around 9 mm if i remember right . just make sure it has two needles for tuning.and the linkage will work for you.

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RE: Ryobi 31 cc Conversion - 9/9/2006 6:14 PM   
davewallace


 

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Status: offline 		dawarrenga,
Any good Walbro will do, with a 28 (28/64th = 11.1mm)cast into the inlet opening of the carb. Here is a link with a bunch of model numbers to go by.

Dave

http://www.prestwich.ndirect.co.uk/walbrocarbs.htm

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RE: Ryobi 31 cc Conversion - 9/9/2006 6:52 PM   
captinjohn


 

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Status: offline 		to change the 28 to a decimal divide 28 by 64= .4375. or 11.1 MM. Capt,n

< Message edited by captinjohn -- 9/9/2006 6:53 PM >

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RE: Ryobi 31 cc Conversion - 9/11/2006 7:14 PM   
Bill Rademacher



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Just curious, what kind of rpms are you all getting?

With a ryobi 31, CH ignition, stock carb, I get about 6400 with a top flight powerpoint 18 X 8 prop.

thanks

bill

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RE: Ryobi 31 cc Conversion - 9/11/2006 9:38 PM   
av8tor1977



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Status: offline 		It's probably not broken in yet if it was new or you put in a new piston ring. You need to change the carb however. The stock carb is very tiny. A carb with an 11mm venturi would be best. Also, do you have a nice free breathing muffler on it?

I'm going to get mine out and run it some more to break it in today, but first run it turned an 18 x 6 Power Point at 7000. I'm hoping it comes up to at least 7500 on that prop, and according to the performance others report, it should do that if not more.

AV8TOR

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RE: Ryobi 31 cc Conversion - 9/11/2006 10:20 PM   
Bill Rademacher



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Thanks!

It is a new motor, with dual Frank Bowman rings, and a Bennet muffler.

I have larger carbs, so I'll try one of those. it pulls the plane pretty well, but I'd like ot get it in the ballpark with other people's motors.

It lends itself pretty well to scale projects of the 120 size.

Bill

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RE: Ryobi 31 cc Conversion - 9/12/2006 1:00 AM   
av8tor1977



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Status: offline 		Yeah, it is definitely not known for being a powerhouse, but it fits a lot of scale cowls so nicely. That's why I did mine for in my Tiger Moth biplane. Nothing sticks out of the cowl and that looks so much better!

A larger carb should definitely help. You could also trade off a little static thrust for speed by going to a 16 x 8 prop on it for now; until it breaks in. That lessens the load a bit and makes it a little easier for the engine break in, especially in a cowled situation where it might try to run a little warm. I doubt you do much hovering or other 3D antics with this ship, so you might like the 16 x 8 in any case as you won't miss the lost thrust, and the extra speed offered by that prop will allow you to throttle back and cruise, and make a high speed pass when you want to do so. Most people use about an 18 x 8 on this engine, but it never hurts to experiment until you come up with a combo you like. Just keep it under 8000 rpms. It may turn the 16 x 8 more than that once it's got a bigger carb and is broken in.

Another thing is the brand of prop. An APC prop is more efficient and what I normally run on everything. It's just that on my big Fokker and Tiger Moth, the wood props look so much nicer....

AV8TOR

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RE: Ryobi 31 cc Conversion - 9/12/2006 2:01 AM   
Bill Rademacher



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Status: offline 		yeah, I like APC props as well, and I have an 18 X 8, but I can't bring myself to cut up the custome spinner for it to fit.

I'll experiment with props, after I see what venturi is on the current carb.

thanks

Bill

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RE: Ryobi 31 cc Conversion - 9/12/2006 6:43 AM   
captinjohn


 

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Status: offline 		I read that bigger APC props are not that good as smaller ones. They say to try a prop called xoar...I guess they really pull hard. More thrust!!!! Capt,n P. S. Desert Aircraft may have em

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RE: Ryobi 31 cc Conversion - 9/12/2006 8:45 AM   
av8tor1977



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Status: offline 		I took my own advice and put an APC 16 x 8 prop on my Ryobi in the Tiger Moth today. The engine is still breaking in with only about 4 tanks of fuel through it, and it's still puking out some black slop so I know it's not "there" yet. But it just sounded like it was lugging a bit with the 18" prop even though it came up to about 7300 rpms. It turns the 16 x 8 prop at about 7600, and the engine just sounds happier. I know I'll like the extra speed as before the Tiger Moth was flying near full throttle all the time. Now I should be able to throttle back and cruise like I mentioned, with that extra in reserve for when I want to do a maneuver. We'll see how it does with more run (break in) time. Then I may go back to the 18" prop.

Static thrust increases with prop diameter and lessened pitch, but I swear the APC 16 x 8 pulls harder than the Top Flite 18 x 6. I didn't take the time to dig out my fish scale, but it sure seemed to be pulling noticeable harder on my tie down rope!! Now to find the time to get it out and test fly it again!

AV8TOR

< Message edited by av8tor1977 -- 9/12/2006 8:50 AM >

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RE: Ryobi 31 cc Conversion - 9/12/2006 8:56 AM   
av8tor1977



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Status: offline 		Bill.... experiment with different props without the spinner until it flies the way you want it to, and then figure out the spinner problem!




AV8TOR

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RE: Ryobi 31 cc Conversion - 9/12/2006 7:12 PM   
Bill Rademacher



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I have run a 16X8 APC, and a 17X6 APC, but the 18X8 Top Flite has done the best so far.

My next step is to pull the motor, and check the venturi on the carb, to make sure of the size.

My target is an 11 mm venturi. Once I have that straight, I'll try different props.


Just curious, what is the largest venturi the motor will tolerate?

thanks

Bill




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RE: Ryobi 31 cc Conversion - 9/12/2006 7:48 PM   
av8tor1977



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Status: offline 		There are some guys running 13mm carbs, but personally I think that's overkill. The reed is only going to flow so much. I would say 11mm is optimal.

Just my opinion however.

AV8TOR

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